The present invention relates to a motor drive apparatus for a surveying instrument and a control method for controlling a surveying instrument, and in particular to a motor drive apparatus and a control method to rotate an instrument axis of the surveying instrument.
In surveying, various kinds of surveying instruments, such as tacheometers, theodolites or total stations, are commonly used for measuring distances and/or angles of objects. Conventionally, these surveying instruments comprise a base having a stand to stably position the surveying instrument on the ground and a head that may be moved with respect to the base. The head generally comprises an optical device, such as a ranging device or sighting device for sighting or focusing on an object, for instance a lens, telescope, camera or the like. In particular, in order for the head to be positionable so as to sight an object, it has to be rotatable in space, preferably in vertical and horizontal direction.
The movable or rotatable head may comprise a ranging device or sighting device for targeting a remote object to determine the location of the remote object. Different kinds of gears are known for rotating the head relative to the base in a horizontal plane, wherein, for example, the ranging device of the head may be provided on a gimbaled yoke to be also movable in vertical direction.
In surveying instruments, such as geodesic-measuring instruments, the rotation of the head may be effected by using a motor, such as DC gear motors so that the head may be adjusted relative to the base.
While it is preferred to rotate the head in short time, it is even more important to provide high accuracy when adjusting a specific angle, wherein the accuracy of angular resolution is preferable below 1″, i.e. fast and highly precise adjusting of an angle is desired.
Existing solutions provide a friction clutch for supporting switching between two operations, namely a first operation, in which the head may be moved manually and quickly and a second operation, in which the head may be moved finely by manually turning a knob, when the clutch is engaged.